Precision coating of viscous liquids and use in forming laminates

ABSTRACT

A process including providing a coating head having an external opening in flow communication with a source of a first coating liquid, positioning the coating head relative to a substrate to define a gap between the external opening and the substrate, creating relative motion between the coating head and the substrate in a coating direction, and dispensing a predetermined quantity of the first coating liquid from the external opening onto at least a portion of at least one major surface of the substrate to form a discrete patch of the first coating liquid in a predetermined position on at least a portion of the major surface of the substrate. The first coating liquid as dispensed exhibits a viscosity of at least 1 Pascal-sec. In some exemplary embodiments, the first coating liquid is a liquid optically clear adhesive composition used in a laminate including a light emitting or reflecting device component.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/734,221, filed Dec. 6, 2012, the disclosure of which is incorporatedby reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to the application of coatingsto substrates, and more particularly to the precise coating ontosubstrates of viscous liquid adhesives that do not self-level, andforming laminates from such coated substrates.

BACKGROUND

Liquid optically clear adhesives (LOCA) are becoming more prevalent inthe display industry to fill the air gap between the optical elements.For example, LOCAs can fill the air gap between a cover glass and indiumtin oxide (ITO) touch sensors, between ITO touch sensors and a liquidcrystal module, or directly between the cover glass and the liquidcrystal module. Recently, several coating processes have been developedfor more precisely coating patches of low to moderate viscosity,self-leveling liquids, such as liquid optically clear adhesives (LOCA),onto substrates.

One known process for applying LOCA patches to a substrate makes use offlowable liquid OCAs that behave like low viscosity Newtonian liquids atthe application conditions. To prevent flow beyond the desired printingarea due to self-leveling of these liquids, the use of a pre-cured dammaterial (matching the refractive index of the LOCA) is often required.This involves an additional process step, and may still potentially leadto overflow of the LOCA if a sufficiently precise amount is notdispensed and/or there is not perfect co-planarity between the twosubstrates that are being bonded with the LOCA.

The use of a screen for precise printing LOCA patches has also beendescribed, for example in Kobayashi et al. (U.S. Patent Application Pub.No. 2009/0215351). Additionally, the use of a stencil for preciseprinting of LOCA patches has been described in PCT International Pub.No. WO 2012/036980. Regardless of whether a screen or a stencil is used,self-leveling of the low to moderate viscosity LOCA may degrade thedesired positional accuracy of the LOCA patch placement on thesubstrate. Nevertheless, such adhesives and processes have been founduseful in forming optical assemblies for producing display panels usedin a variety of electronic devices.

SUMMARY

In one aspect, the present disclosure describes a process includingproviding a coating head having an external opening in flowcommunication with a source of a first coating liquid, positioning thecoating head relative to a substrate to define a gap between theexternal opening and the substrate, creating relative motion between thecoating head and the substrate in a coating direction, and dispensing apre-determined quantity of the first coating liquid from the externalopening onto at least a portion of at least one major surface of thesubstrate to form a discrete patch of the first coating liquid in apredetermined position on at least a portion of the major surface of thesubstrate. The patch has a thickness and a perimeter. The first coatingliquid as dispensed exhibits a viscosity of at least 1 Pascal-sec. Thefirst coating liquid can be a liquid optically clear adhesive (LOCA)composition. It is presently preferred that a screen or stencil is notused to form the discrete patch.

LISTING OF EXEMPLARY EMBODIMENTS

In some exemplary embodiments of the foregoing coating processes, thefirst coating liquid is dispensed at a shear rate of at least about 1sec⁻¹. In other exemplary embodiments, the first coating liquid isdispensed at a shear rate of at least about 10, about 50, about 100,about 1000, and about 10000 sec⁻¹. Optionally, the first coating liquidis dispensed at a shear rate no greater than about 100,000 sec⁻¹. Incertain exemplary embodiments, the first coating liquid is dispensed ata temperature from about 20° C. to about 100° C. In some such exemplaryembodiments, the first coating liquid as dispensed exhibits a viscosityfrom about 2 Pascal-sec to about 20 Pascal-sec.

In further exemplary embodiments of any of the foregoing coatingprocesses, the first coating liquid exhibits at least one distinguishingrheological characteristic selected from thixotropic rheologicalbehavior and pseudoplastic rheological behavior. In certain exemplaryembodiments, the first coating liquid exhibits a Thixotropic Index,defined as the ratio of the low shear viscosity measured at a shear rateof 0.1 sec⁻¹ to the high shear viscosity measured at 100 sec⁻¹, of atleast 5. In some exemplary embodiments, the first coating liquidexhibits an Equilibrium Viscosity measured on a coating liquid in afully relaxed state at a shear rate of 1 sec⁻¹ sufficiently high toprevent self-leveling of the coating liquid on the substrate.Optionally, the Equilibrium Viscosity measured at a shear rate of 0.01sec⁻¹ is at least 80 Pa-sec.

In additional exemplary embodiments of any of the foregoing coatingprocesses, the first coating liquid is a liquid optically clear adhesivecomposition. In some such embodiments, the liquid optically clearadhesive composition includes a reaction product of a multifunctional(meth)acrylate oligomer and a reactive diluent including amonofunctional (meth)acrylate monomer having a viscosity of from 0.004to 0.020 Pascal-sec measured at a shear rate of 1 sec⁻¹ and atemperature of 25° C., and at least one of a plasticizer or amonofunctional (meth)acrylate monomer having alkylene oxidefunctionality. In certain exemplary embodiments of any of the foregoingcoating processes, the multifunctional (meth)acrylate oligomer includesany one or more of a multifunctional urethane (meth)acrylate oligomer, amultifunctional polyester (meth)acrylate oligomer, and a multifunctionalpolyether (meth)acrylate oligomer.

In other exemplary embodiments of any of the foregoing coatingprocesses, the liquid optically clear adhesive composition includes areaction product of a multifunctional rubber-based (meth)acrylateoligomer and a monofunctional (meth)acrylate monomer having a pendantalkyl group of from about 4 to 20 carbon atoms, and a liquid rubber. Incertain such exemplary embodiments, the multifunctional rubber-based(meth)acrylate oligomer comprises any one or more of a multifunctionalpolybutadiene (meth)acrylate oligomer, a multifunctional isoprene(meth)acrylate oligomer, and a multifunctional (meth)acrylate oligomerincluding a copolymer of butadiene and isoprene. Optionally, the liquidrubber includes liquid isoprene.

In further exemplary embodiments of any of the foregoing coatingprocesses, the liquid optically clear adhesive composition is a curablecomposition including (a) a (meth)acryolyl oligomer having a M_(w) of 5to 30 kDa and a T_(g) of less than 20° C. including: (i.) greater than50 parts by weight of (meth)acrylate ester monomer units, (ii.) 10 to 49parts by weight of hydroxyl-functional monomer units, (iii.) 1 to 10parts by weight of monomer units having pendent (meth)acrylate groups,(iv.) 0 to 20 parts by weight of polar monomer units, (v.) 0 to 10 partsby weight of silane-functional monomer units, wherein the sum of themonomer units is 100 parts by weight; (b) a diluent monomer component;and (c) a photoinitiator. The curable composition preferably includes nocross-linking agents. In certain such embodiments, the diluent monomercomponent comprises at least one monomer selected from (meth)acrylateester monomer units, hydroxyl-functional monomer units; monomer unitshaving pendent (meth)acrylate groups, polar monomer units, andsilane-functional monomer units.

In any of the foregoing exemplary coating processes, the liquidoptically clear adhesive composition further includes at least oneadditive selected from heat stabilizers, antioxidants, antistaticagents, thickeners, fillers, pigments, dyes, colorants, thixotropicagents, processing aids, nanoparticles, and fibers. In certain suchembodiments, the additive is present in an amount of 0.01 to 10 wt. %relative to the mass of the liquid optically clear adhesive composition.In some such exemplary embodiments, the liquid optically clear adhesivecomposition further includes metal oxide nanoparticles having a medianparticle diameter of 1 nm to about 100 nm in an amount of 1 to 10 wt. %,relative to the total weight of the liquid optically clear adhesivecomposition.

In any of the foregoing exemplary embodiments coating processes, thepatch covers only a portion of a first major surface of the substrate.In some exemplary embodiments of any of the foregoing coating processes,the perimeter exhibits a geometric shape selected from a square, arectangle, or a parallelogram. In certain exemplary embodiments of anyof the foregoing coating processes, the predetermined position isselected such that the perimeter of the patch has a center proximate acenter of the major surface of the substrate.

In further exemplary embodiments of any of the foregoing coatingprocesses, the thickness of the patch is non-uniform. In some suchembodiments, the thickness of the patch is greater proximate the centerof the patch, and the thickness of the patch is lower proximate theperimeter of the patch. In certain embodiments, the patch includes atleast one raised discrete protrusion extending outwardly from the majorsurface of the substrate. In further such exemplary embodiments, the atleast one raised discrete protrusion is comprised of at least one raisedrib extending across at least a portion of the major surface of thesubstrate. In some such embodiments, the at least one raised ribincludes at least two raised ribs arranged cross-wise on the majorsurface of the substrate. In certain such embodiments, the at least tworibs intersect and overlap proximate the center of the perimeter of thepatch.

In other exemplary embodiments coating processes, the at least oneraised discrete protrusion is a multiplicity of raised discreteprotrusions. In some such exemplary embodiments, the multiplicity ofraised discrete protrusions is selected from a plurality of raiseddiscrete bumps, a multiplicity of raised discrete ribs, or a combinationthereof. In certain such embodiments, the multiplicity of raiseddiscrete bumps is comprised of hemispherically-shaped bumps. Optionally,the multiplicity of raised discrete bumps is arranged in an arraypattern. In some particular embodiments, the multiplicity of raiseddiscrete ribs form a dogbone-shaped pattern.

In other exemplary embodiments of any of the foregoing coatingprocesses, the multiplicity of raised discrete ribs is comprised ofelliptically-shaped ribs. In some such embodiments, the multiplicity ofraised discrete ribs is arranged such that each rib is arrangedsubstantially parallel to each adjoining rib. In certain suchembodiments, at least two of the multiplicity of raised discrete ribsare arranged substantially parallel to each other, and at least one ofthe multiplicity of raised discrete ribs is arranged substantiallyorthogonal to the at least two substantially parallel raised discreteribs.

In alternative exemplary embodiments to those described in the precedingtwo paragraphs, the thickness of the patch is substantially uniform.Optionally, a mean thickness of the patch is from about 1 μm to about500 μm. In some such exemplary embodiments, the thickness of the patchhas a uniformity of +/−10% of the mean thickness or better.

In further exemplary embodiments of any of the foregoing coatingprocesses, the perimeter of the patch is defined by a plurality oflateral edges of the patch. In some such embodiments, at least onelateral edge of the patch is positioned relative to an edge of thesubstrate to within +/−500 μm of a target position.

In additional exemplary embodiments of any of the foregoing coatingprocesses, the substrate is a light emitting display component or alight reflecting device component. In some exemplary embodiments, thesubstrate is substantially transparent. In certain exemplaryembodiments, the substrate is comprised of glass. In some particularembodiments, the substrate is flexible.

In additional exemplary embodiments of any of the foregoing coatingprocesses, the coating head is selected from the group consisting of asingle slot die, a multiple slot die, a single orifice die, and amultiple orifice die. In certain such embodiments, the coating head is asingle slot die having a single die slot, further wherein the externalopening is comprised of the die slot. In some particular suchembodiments, the geometry of the single slot die is selected from asharp-lipped extrusion slot die, a slot fed knife die with a land, or anotched slot die.

In any of the foregoing exemplary embodiments of coating processes, thesource of the first coating liquid comprises a pre-metered coatingliquid delivery system selected from a syringe pump, a dosing pump, agear pump, a servo-driven positive displacement pump, a rod-drivenpositive displacement pump, or a combination thereof.

In some particular exemplary embodiments of the foregoing coatingprocesses, at least one pressure sensor communicating with the source ofthe first coating liquid is used to measure a delivery pressure of thefirst coating liquid. The delivery pressure is used to control at leastone of the delivery rate of the first coating liquid to the substrate,or a quality characteristic of the patch. Suitable qualitycharacteristics include the thickness uniformity of the patch, thepositional accuracy and/or precision of the patch position on thesubstrate relative to a target position (as described further below),the uniformity of the patch perimeter (e.g., the “squareness” of a patchhaving a square-shaped perimeter), the straightness of an edge of thepatch, the absence of coating defects (e.g., bubbles, voids, entrainedforeign matter, surface irregularities, and the like), the quantity(e.g., by weight or volume) of the first coating liquid forming thepatch, and the like.

In further exemplary embodiments, the coating process includes repeatingthe steps of paragraph [0006] using a second coating liquid. In certainsuch exemplary embodiments, a second coating liquid different from thefirst coating liquid is used. In other such exemplary embodiments, asecond coating liquid which is the same as the first coating liquid isused. In any of the foregoing exemplary embodiments, the second coatingliquid can overlay at least a portion of the first coating liquid.

In additional further exemplary embodiments of any of the foregoingprocesses, the process further includes disposing a second substraterelative to the first substrate such that the patch is positionedbetween the first and second substrates, wherein the patch contacts atleast a portion of each of the first and second substrates, therebyforming a laminate. In some such embodiments, the process furtherincludes curing the coating liquid by applying heat, actinic radiation,ionizing radiation, or a combination thereof. In some particularexemplary embodiments, the laminate includes an organic light-emittingdiode display, an organic light-emitting transistor display, a liquidcrystal display, a plasma display, a surface-conduction electron-emitterdisplay, a field emission display, a quantum dot display, a liquidcrystal display, a micro-electromechanical system display, a ferroliquid display, a thick-film dielectric electroluminescent display, atelescopic pixel display, or a laser phosphor display.

Various aspects and advantages of exemplary embodiments of thedisclosure have been summarized. The above Summary is not intended todescribe each illustrated embodiment or every implementation of thepresent certain exemplary embodiments of the present disclosure. TheDrawings and the Detailed Description that follow more particularlyexemplify certain preferred embodiments using the principles disclosedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an exemplary coating apparatus.

FIG. 2A is a top view of a portion of a sheet of substrate materialhaving disposed thereon an exemplary patch of coated liquid.

FIG. 2B is a top view of a section along the length of a web ofindefinite length material having disposed thereon a series of patchesof coated liquid.

FIG. 2C is a side view of a portion of a sheet of substrate materialhaving an exemplary patch of coated liquid having a deliberatelynon-uniform side profile disposed on it.

FIG. 2D is a top view of the coated sheet of FIG. 2C.

FIG. 2E is a side view of a portion of a sheet of substrate materialhaving disposed thereon an intentionally non-uniform patch of coatedliquid exhibiting an exemplary non-uniform side profile of twoelliptically-shaped ribs arranged in a crosswise manner substantiallyorthogonal to each other.

FIG. 2F is a top view of the coated sheet of FIG. 2E.

FIG. 2G is a top view of a portion of a sheet of substrate materialhaving disposed thereon an intentionally non-uniform patch of coatedliquid exhibiting an exemplary non-uniform side profile of a pluralityof substantially parallel elliptically-shaped ribs arranged on a majorsurface of the substrate

FIG. 2H is a top view of a portion of a sheet of substrate materialhaving disposed thereon an intentionally non-uniform patch of coatedliquid exhibiting an exemplary non-uniform side profile of a pluralityof substantially parallel elliptically-shaped ribs arranged on a majorsurface of the substrate, and a single rib arranged in a crosswisemanner substantially orthogonal to the plurality of substantiallyparallel elliptically-shaped ribs.

FIG. 3 is a photograph of a substrate with a recently coated patch ofliquid thereon, showing an instance where the coating bead is beingbroken at the trailing end of the patch relatively quickly.

FIG. 4 is a photograph of a substrate with a recently coated patch ofliquid thereon, showing an instance where the coating bead is beingbroken at the trailing end of the patch relatively slowly.

FIG. 5 is a photograph of a substrate with a recently coated patch ofliquid thereon having, undesirable margin on the leading edge due tocompressibility in the liquid delivery system.

FIG. 6 is a photograph of a substrate with a recently coated patch ofliquid thereon, having undesirable margin on the leading edge of onepatch and the trailing edge of an adjacent patch due to a bubble in thedie cavity.

In the drawings, like reference numerals indicate like elements. Whilethe above-identified drawing, which may not be drawn to scale, setsforth various embodiments of the present disclosure, other embodimentsare also contemplated, as noted in the Detailed Description. In allcases, this disclosure describes the presently disclosed invention byway of representation of exemplary embodiments and not by expresslimitations. It should be understood that numerous other modificationsand embodiments can be devised by those skilled in the art, which fallwithin the scope and spirit of this invention.

DETAILED DESCRIPTION

Recently, a liquid optically clear adhesive (LOCA) composition wasdisclosed in PCT International Pub. No. WO 2011/119828. An example ofcoating a patch of this LOCA composition onto a display substrate usinga stencil to determine the perimeter of the patch was disclosed in PCTInternational Pub. No. WO 2012/036980. In addition to the positionalaccuracy and throughput limitations imposed by use of a stencil, it isusually necessary to provide for prompt, in-line vacuum lamination ofthe LOCA-coated substrate in order to prevent the entrapment of bubblesbetween the layers. Further, such vacuum lamination may require apreliminary partial cure at the periphery of the patch to prevent theLOCA from slumping or “oozing-out” of the initially-defined patchperimeter due to the self-leveling characteristics of the LOCA afterremoval of the stencil. Such slumping or “oozing-out” disadvantageouslydegrades the positional accuracy of patch placement on the substrate.

The present disclosure describes methods of coating a liquid onto asubstrate, and in particular methods of coating a LOCA onto a rigidsubstrate (e.g., cover glass, indium tin oxide (ITO) touch sensor stack,polarizer, liquid crystal module, and the like) without the assistanceof a printing aid (e.g., a screen, a mask, a stencil, a pre-cured dam),which at least partially overcome some or all of these deficiencies. Themethods, which do not generally make use of a stencil, have been usedfor coating of precisely-positioned patches of high viscosity(preferably pseudoplastic and/or thixotropic) liquid compositions ontotarget substrates without substantial self-leveling or “oozing-out” ofthe patch on the substrate surface prior to application of a subsequentlamination step.

In particular, it has been found that die coating methods can beemployed to dispose liquid optically clear compositions, such asadhesives and more particularly LOCA's, accurately and quickly inprecision lamination applications involving gap filling between a basesubstrate (e.g., a display panel) and a cover substrate. Suchapplications include the lamination of a glass panel onto a displaypanel in LCD displays, or the lamination of a touch sensitive panel ontoa display panel in touch-sensitive electronic devices.

The presently disclosed processes, can, in exemplary embodiments, permitsignificant improvements in throughput in a coating and laminationprocess by reducing cycle times and improving yields. Exemplary methodsof the present disclosure can permit the precise positioning of anon-self-leveling liquid patch on a substrate surface with respect to atarget position, achieving positional accuracy of the patch placementwhich has heretofore has not been obtainable in a consistent manner.Some exemplary methods of the present disclosure may be used toprecisely coat a liquid optically clear adhesive onto a rigid substratewithout the use of a pattern or a printing aid, such as a stencil,screen, mask or dam.

For the following Glossary of defined terms, these definitions shall beapplied for the entire application, unless a different definition isprovided in the claims or elsewhere in the specification.

GLOSSARY

Certain terms are used throughout the description and the claims that,while for the most part are well known, may require some explanation. Itshould understood that, as used herein:

The term “homogeneous” means exhibiting only a single phase of matterwhen observed at a macroscopic scale.

The term “liquid optically clear adhesive composition” means a liquidoptically clear adhesive (LOCA) or a precursor composition which may becured to form a LOCA.

The term “pseudoplasticity” or “pseudoplastic” with respect to a coatingliquid means that the coating liquid exhibits a viscosity whichdecreases with increasing shear rate.

The term “thixotropy” or “thixotropic” with respect to a coating liquidmeans that the coating liquid exhibits a viscosity which decreases withincreasing shearing time for the time interval during which the coatingliquid undergoes shear during the process of applying the coating liquidto the substrate. Thixotropic coating fluids recover or “build”viscosity to at least the static viscosity upon cessation of shearing,e.g. after the coating liquid is applied to a substrate.

The term “Thixotropic Index” is a coating liquid property that refers tothe ratio of the low shear viscosity measured at a shear rate of 0.1sec⁻¹ to the high shear viscosity measured at 100 sec⁻¹.

The term “Equilibrium Viscosity” is a coating liquid property thatrefers to the viscosity of a coating fluid measured from a fully-relaxed(i.e., equilibrium) condition at a shear rate of 1.0 sec⁻¹, unless adifferent shear rate is expressly specified in association with aparticular Equilibrium Viscosity value.

The terms “(co)polymer” or “(co)polymers” includes homopolymers andcopolymers, as well as homopolymers or copolymers that may be formed ina miscible blend, e.g., by coextrusion or by reaction, including, e.g.,transesterification. The term “copolymer” includes random, block andstar (e.g., dendritic) copolymers.

The term “(meth)acrylate” with respect to a monomer, oligomer or means avinyl-functional alkyl ester formed as the reaction product of analcohol with an acrylic or a methacrylic acid.

The term “glass transition temperature” or “T_(g)” refers to the glasstransition temperature of a (co)polymer when evaluated in bulk ratherthan in a thin film form. In instances where a (co)polymer can only beexamined in thin film form, the bulk form T_(g) can usually be estimatedwith reasonable accuracy. Bulk form T_(g) values usually are determinedby evaluating the rate of heat flow vs. temperature using differentialscanning calorimetry (DSC) to determine the onset of segmental mobilityfor the copolymer and the inflection point (usually a second-ordertransition) at which the copolymer can be said to change from a glassyto a rubbery state. Bulk form T_(g) values can also be estimated using adynamic mechanical thermal analysis (DMTA) technique, which measures thechange in the modulus of the copolymer as a function of temperature andfrequency of vibration.

The term “adjoining” with reference to a particular layer means joinedwith or attached to another layer, in a position wherein the two layersare either next to (i.e., adjacent to) and directly contacting eachother, or contiguous with each other but not in direct contact (i.e.,there are one or more additional layers intervening between the layers).

By using terms of orientation such as “atop”, “on”, “covering”,“uppermost”, “underlying” and the like for the location of variouselements in the disclosed coated articles, we refer to the relativeposition of an element with respect to a horizontally-disposed,upwardly-facing substrate. Unless otherwise indicated, it is notintended that the substrate or articles should have any particularorientation in space during or after manufacture.

By using the term “overcoated” to describe the position of a layer withrespect to a substrate or other element of an article of the presentdisclosure, we refer to the layer as being atop the substrate or otherelement, but not necessarily contiguous to either the substrate or theother element.

By using the term “separated by” to describe the position of a layerwith respect to other layers, we refer to the layer as being positionedbetween two other layers but not necessarily contiguous to or adjacentto either layer.

The terms “about” or “approximately” with reference to a numerical valueor a shape means+/−five percent of the numerical value or property orcharacteristic, but expressly includes the exact numerical value. Forexample, a viscosity of “about” 1 Pa-sec refers to a viscosity from 0.95to 1.05 Pa-sec, but also expressly includes a viscosity of exactly 1Pa-sec. Similarly, a perimeter that is “substantially square” isintended to describe a geometric shape having four lateral edges inwhich each lateral edge has a length which is from 95% to 105% of thelength of any other lateral edge, but which also includes a geometricshape in which each lateral edge has exactly the same length.

The term “substantially” with reference to a property or characteristicmeans that the property or characteristic is exhibited to a greaterextent than the opposite of that property or characteristic isexhibited. For example, a substrate that is “substantially” transparentrefers to a substrate that transmits more radiation (e.g., visiblelight) than it fails to transmit (e.g., absorbs and reflects). Thus, asubstrate that transmits more than 50% of the visible light incidentupon its surface is substantially transparent, but a substrate thattransmits 50% or less of the visible light incident upon its surface isnot substantially transparent.

As used in this specification and the appended embodiments, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. Thus, for example, reference to fine fiberscontaining “a compound” includes a mixture of two or more compounds. Asused in this specification and the appended embodiments, the term “or”is generally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

As used in this specification, the recitation of numerical ranges byendpoints includes all numbers subsumed within that range (e.g. 1 to 5includes 1, 1.5, 2, 2.75, 3, 3.8, 4, and 5).

Unless otherwise indicated, all numbers expressing quantities oringredients, measurement of properties and so forth used in thespecification and embodiments are to be understood as being modified inall instances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the foregoingspecification and attached listing of embodiments can vary dependingupon the desired properties sought to be obtained by those skilled inthe art utilizing the teachings of the present disclosure. At the veryleast, and not as an attempt to limit the application of the doctrine ofequivalents to the scope of the claimed embodiments, each numericalparameter should at least be construed in light of the number ofreported significant digits and by applying ordinary roundingtechniques.

Exemplary embodiments of the present disclosure may take on variousmodifications and alterations without departing from the spirit andscope of the present disclosure. Accordingly, it is to be understoodthat the embodiments of the present disclosure are not to be limited tothe following described exemplary embodiments, but is to be controlledby the limitations set forth in the claims and any equivalents thereof.

Exemplary Coating Processes

The present disclosure describes a process including the steps ofproviding a coating head having an external opening in flowcommunication with a source of a first coating liquid, positioning thecoating head relative to a substrate to define a gap between theexternal opening and the substrate, creating relative motion between thecoating head and the substrate in a coating direction, and dispensing apre-determined quantity of the first coating liquid from the externalopening onto at least a portion of at least one major surface of thesubstrate to form a discrete patch of the first coating liquid in apredetermined position on at least a portion of the major surface of thesubstrate. The first coating liquid as dispensed exhibits a viscosity ofat least 1 Pascal-sec (Pa-s). The patch has a thickness and a perimeter.It is presently preferred that a stencil is not used to form thediscrete patch.

In further exemplary embodiments, the process includes repeating thesteps of the immediately preceding paragraph. In certain such exemplaryembodiments, a second coating liquid different from the first coatingliquid can be used. In other exemplary embodiments, a second coatingliquid which is the same as the first coating liquid is used. In any ofthe foregoing exemplary embodiments, the second coating liquid canoverlay at least a portion of the first coating liquid.

In some exemplary embodiments, the first coating liquid is dispensed ata shear rate of at least about 100 sec⁻¹, 200 sec⁻¹, 300 sec⁻¹, 400sec⁻¹, 500 sec⁻¹, 600 sec⁻¹, 700 sec⁻¹, 800 sec⁻¹, 900 sec⁻¹, or even ata shear rate of at least about 1,000 sec⁻¹, 2,000 sec⁻¹, 3,000 sec⁻¹,4,000 sec⁻¹, 5,000 sec⁻¹, 10,000 sec⁻¹, or even higher shear rate. Incertain such exemplary embodiments, the first coating liquid isdispensed at a shear rate no greater than about 1,000,000 sec⁻¹, 750,000sec⁻¹, 600,000 sec⁻¹, 500,000 sec⁻¹, 400,000 sec⁻¹, 300,000 sec⁻¹,250,000 sec⁻¹, 200,000 sec⁻¹, or even 100,000 sec⁻¹.

In any of the foregoing embodiments, the first coating liquid isdispensed at a temperature from at least about 20° C., 30° C., 40° C.,or 50° C.; and at most about 100° C., 90° C., 80° C., 70° C., or even60° C.

Exemplary Coating Liquids

In presently preferred embodiments, the first coating liquid asdispensed exhibits a viscosity measured at a shear rate of 100 sec⁻¹ anda temperature of 25° C., of at least 1 Pascal-sec (Pa-s). However, insome exemplary embodiments, the coating liquid may advantageouslyexhibit a viscosity of at least 2 Pa-s, at least 3 Pa-s, at least 4Pa-s, at least 5 Pa-s, at least 6 Pa-s, at least 7 Pa-s, at least 8Pa-s, at least 9 Pa-s, or even at least 10 Pa-s, at least 15 Pa-s, atleast 20 Pa-s, at least 30 Pa-s, at least 40 Pa-s, at least 50 Pa-s oreven higher viscosity.

In certain such exemplary embodiments, the first coating liquid asdispensed exhibits a viscosity measured at a shear rate of 100 sec⁻¹ anda temperature of 25° C. of no greater than 1,000 Pa-s, no greater than500 Pa-s, no greater than 400 Pa-s, no greater than 300 Pa-s, or even nogreater than 200 Pa-s.

In some such exemplary embodiments, the first coating liquid asdispensed exhibits a viscosity measured at a shear rate of 100 sec⁻¹ anda temperature of 25° C. from about 2 Pa-s to about 50 Pa-s, 5 Pa-s toabout 20 Pa-s, from about 6 Pa-s to about 19 Pa-s, from about 7 Pa-s toabout 18 Pa-s, from about 8 Pa-s to about 17 Pa-s, from about 9 Pa-s toabout 16 Pa-s, or even from about 10 Pa-s to about 15 Pa-s.

In further exemplary embodiments of any of the foregoing, the firstcoating liquid exhibits at least one distinguishing rheologicalcharacteristic selected from thixotropic rheological behavior andpseudoplastic rheological behavior. In certain exemplary embodiments,the first coating liquid exhibits a Thixotropic Index, defined as theratio of the low shear viscosity measured at a shear rate of 0.1 sec⁻¹to the high shear viscosity measured at 100 sec⁻¹, of at least 3, atleast 4, at least 5, at least 6, at least 7, at least 8, at least 9, atleast 10, or even at least 15, 20 or higher.

In some exemplary embodiments, the first coating liquid exhibits anEquilibrium Viscosity measured on a coating liquid in a fully relaxedstate at a shear rate of 1 sec⁻¹ sufficiently high to preventself-leveling of the coating liquid on the substrate. In certain suchembodiments, the Equilibrium Viscosity measured at a shear rate ofeither 1 sec⁻¹ or 0.01 sec⁻¹ is at least 80 Pa-s 1, 150 Pa-s, 160 Pa-s,170 Pa-s, 180 Pa-s, 190 Pa-s, 200 Pa-s, 225 Pa-s, 250 Pa-s, 300 Pa-s,400 Pa-s, 500 Pa-s, or even 1,000 Pa-s or higher.

Liquid Optically Clear Adhesive Compositions

Particularly suitable liquid compositions for use in the foregoingcoating processes are LOCA compositions, such as adhesives that are usedin making optical assemblies. Thus, in some exemplary embodiments of anyof the foregoing processes, at least one of the first coating liquid andthe second coating liquid (or both) is selected to be a liquid opticallyclear adhesive (LOCA) composition.

In some such exemplary embodiments, the LOCA is a highly viscousNewtonian fluid having a viscosity of at least 1 Pa-s at the coatingshear rate and temperature.

In some exemplary embodiments, the LOCA composition is dispensed at ashear rate of at least about 100 sec⁻¹, 200 sec⁻¹, 300 sec⁻¹, 400 sec⁻¹,500 sec⁻¹, 600 sec⁻¹, 700 sec⁻¹, 800 sec⁻¹, 900 sec⁻¹, or even at ashear rate of at least about 1,000 sec⁻¹, 2,000 sec⁻¹, 3,000 sec⁻¹,4,000 sec⁻¹, 5,000 sec⁻¹, 10,000 sec⁻¹, or even higher shear rate. Incertain such exemplary embodiments, the LOCA composition is dispensed ata shear rate no greater than about 1,000,000 sec⁻¹, 750,000 sec⁻¹,600,000 sec⁻¹, 500,000 sec⁻¹, 400,000 sec⁻¹, 300,000 sec⁻¹, 250,000sec⁻¹, 200,000 sec⁻¹, or even 100,000 sec⁻¹.

In any of the foregoing embodiments, the LOCA composition is dispensedat a temperature from at least about 20° C., 30° C., 40° C., or 50° C.;and at most about 100° C., 90° C., 80° C., 70° C., or even 60° C.

In presently preferred embodiments, the LOCA composition as dispensedexhibits a viscosity measured at a shear rate of 100 sec⁻¹ and atemperature of 25° C., of at least 1 Pascal-sec (Pa-s). However, in someexemplary embodiments, the LOCA composition may advantageously exhibit aviscosity of at least 2 Pa-s, at least 3 Pa-s, at least 4 Pa-s, at least5 Pa-s, at least 6 Pa-s, at least 7 Pa-s, at least 8 Pa-s, at least 9Pa-s, or even at least 10 Pa-s, at least 15 Pa-s, at least 20 Pa-s, atleast 30 Pa-s, at least 40 Pa-s, at least 50 Pa-s or even higherviscosity.

In certain such exemplary embodiments, the LOCA composition as dispensedexhibits a viscosity measured at a shear rate of 100 sec⁻¹ and atemperature of 25° C. of no greater than 1 MPa-s, no greater than 500Pa-s, no greater than 400 Pa-s, no greater than 300 Pa-s, or even nogreater than 200 Pa-s.

In some such exemplary embodiments, the LOCA composition as dispensedexhibits a viscosity measured at a shear rate of 100 sec⁻¹ and atemperature of 25° C. from about 2 Pa-s to about 50 Pa-s, 5 Pa-s toabout 20 Pa-s, from about 6 Pa-s to about 19 Pa-s, from about 7 Pa-s toabout 18 Pa-s, from about 8 Pa-s to about 17 Pa-s, from about 9 Pa-s toabout 16 Pa-s, or even from about 10 Pa-s to about 15 Pa-s.

In some exemplary embodiments, the LOCA composition preferably exhibitspseudoplastic and/or thixotropic rheological behavior. Such LOCAcompositions exhibit a solid like behavior at little to no shear (e.g.at least about 500 Pa-s at 0.01 s⁻¹), while being flowable during thecoating process when a higher amount of shear is applied (e.g. less morethan 1 Pa-s but less than about 500 Pa-s at about 1-5,000 s⁻¹).Pseudoplastic LOCA compositions exhibit shear thinning rheologicalbehavior in which the viscosity decreases with increasing shear rate toreach a high shear rate (e.g. at a shear rate greater than 1,000 sec⁻¹)limiting viscosity, then recovering to rebuild viscosity upon cessationof shearing. Thixotropic LOCA compositions exhibit time-dependentrheological properties, decreasing in viscosity with increasing shearingduration to reach a limiting viscosity, then recovering to rebuildviscosity within a finite time frame after the cessation of shearing.

The pseudoplastic and/or thixotropic LOCA composition recovers its highviscosity properties within a short time frame (e.g. less than 1 second)after completion of the coating process. In other words, the LOCAcomposition in the coated patch does not substantially self-level,thereby ensuring that dimensional tolerances of the coated patch aremaintained. LOCA compositions that are both pseudoplastic andthixotropic may be particularly useful in practicing exemplary processesof the present disclosure, as such properties help ensure that thedesired positional and dimensional tolerances of the patch coated on thesubstrate are maintained.

Thus, in further exemplary embodiments of the foregoing, the LOCAcomposition exhibits at least one distinguishing rheologicalcharacteristic selected from thixotropic rheological behavior andpseudoplastic rheological behavior. In certain exemplary embodiments,the LOCA composition exhibits a Thixotropic Index, defined as the ratioof the low shear viscosity measured at a shear rate of 0.1 sec⁻¹ to thehigh shear viscosity measured at 100 sec⁻¹, of at least 1, at least 2,at least 3, at least 4, at least 5, at least 6, at least 7, at least 8,at least 9, at least 10, or even at least 15, 20 or higher.

In some exemplary embodiments, the LOCA composition exhibits anEquilibrium Viscosity measured on a coating liquid in a fully relaxedstate at a shear rate of 1 sec⁻¹ sufficiently high to preventself-leveling of the coating liquid on the substrate. In certain suchembodiments, the Equilibrium Viscosity measured at a shear rate of 1sec⁻¹ or 0.01 sec⁻¹ is at least 80 Pa-s, 150 Pa-s, 160 Pa-s, 170 Pa-s,180 Pa-s, 190 Pa-s, 200 Pa-s, 225 Pa-s, 250 Pa-s, 300 Pa-s, 400 Pa-s,500 Pa-s, or even 1,000 Pa-s or higher.

In some embodiments, the LOCA composition has a displacement creep ofabout 0.2 radians or less when a stress of 10 Pa is applied to theadhesive for 2 minutes. Particularly, the LOCA composition has adisplacement creep of about 0.1 radians or less when a stress of 10 Pais applied to the adhesive for 2 minutes. In general, displacement creepis a value determined using an AR2000 Rheometer manufactured by TAInstruments having with a measurement geometry of a 40 mm diameter×1°cone at 25° C., and is defined as the rotational angle of the cone whena stress of 10 Pa is applied to the adhesive. The displacement creep isrelated to the ability of the thixotropic adhesive layer to resist flow,or sag, under very low stress conditions, such as gravity and surfacetension.

In some embodiments, the LOCA composition has a delta of 45 degrees orless, particularly 42 or less, particularly 35 degrees or less and moreparticularly 30 degrees or less when a torque of 80 microN·m is appliedat a frequency of 1 Hz in a cone and plate rheometer. Delta is the phaselag between stress and strain where an oscillatory force (stress) isapplied to a material and the resulting displacement (strain) ismeasured. Delta is assigned units of degrees. The delta is related tothe “solid” behavior of the pseudoplastic and/or thixotropic adhesivelayer or its non-sag property at very low oscillatory stress.

The adhesive layer also has the ability to regain its non-sag structurewithin a short amount of time after passing underneath the coating dieslot. In one embodiment, the recovery time of the adhesive layer is lessthan about 60 seconds, particularly less than about 30 seconds, and moreparticularly less than about 10 seconds to reach a delta of 35 degreesafter a torque of about 1000 microN·m is applied for about 60 seconds ata frequency of 1 Hz and immediately followed by a torque of 80 microN·mat a frequency of 1 Hz.

In some of the foregoing embodiments, the LOCA composition includes areaction product of a multifunctional (meth)acrylate oligomer and areactive diluent including a monofunctional (meth)acrylate monomerhaving a viscosity of from 0.004 to 0.020 Pascal-sec measured at a shearrate of 1 sec⁻¹ and a temperature of 25° C., and at least one of aplasticizer or a monofunctional (meth)acrylate monomer having alkyleneoxide functionality. In certain such exemplary embodiments of any of theforegoing, the multifunctional (meth)acrylate oligomer includes any oneor more of a multifunctional urethane (meth)acrylate oligomer, amultifunctional polyester (meth)acrylate oligomer, and a multifunctionalpolyether (meth)acrylate oligomer.

In other exemplary embodiments of any of the foregoing processes, theLOCA composition includes a reaction product of a multifunctionalrubber-based (meth)acrylate oligomer and a monofunctional (meth)acrylatemonomer having a pendant alkyl group of from about 4 to 20 carbon atoms,and a liquid rubber. In certain such exemplary embodiments, themultifunctional rubber-based (meth)acrylate oligomer comprises any oneor more of a multifunctional polybutadiene (meth)acrylate oligomer, amultifunctional isoprene (meth)acrylate oligomer, and a multifunctional(meth)acrylate oligomer including a copolymer of butadiene and isoprene.Optionally, the liquid rubber includes liquid isoprene.

In further exemplary embodiments of any of the foregoing processes, theLOCA composition is a curable composition including (a) a (meth)acryolyloligomer having a M_(w) of 5 to 30 kDa and a T_(g) of less than 2° C.including: (i.) greater than 50 parts by weight of (meth)acrylate estermonomer units, (ii.) 10 to 49 parts by weight of hydroxyl-functionalmonomer units, (iii.) 1 to 10 parts by weight of monomer units havingpendent acrylate groups, (iv.) 0 to 20 parts by weight of polar monomerunits, (v.) 0 to 10 parts by weight of silane-functional monomer units,wherein the sum of the monomer units is 100 parts by weight; (b) adiluent monomer component; and (c) a photoinitiator. The curablecomposition includes no crosslinking agents. In certain suchembodiments, the diluent monomer component comprises at least onemonomer selected from acrylate ester monomer units, hydroxyl-functionalmonomer units; monomer units having pendent acrylate groups, polarmonomer units, and silane-functional monomer units.

Suitable LOCA compositions are described in PCT International Pub. Nos.WO 2010/111316, WO 2011/119828, WO 2012/036980, and WO 2013/049133; andin U.S. Prov. Pat. App. filed May 29, 2012 under Attorney Docket No.69825US002 and titled “LIQUID OPTICALLY CLEAR ADHESIVE COMPOSITIONS”.

Additives

In any of the foregoing exemplary embodiments, the LOCA composition mayadvantageously include at least one additive selected from heatstabilizers, antioxidants, antistatic agents, thickeners, fillers,pigments, dyes, colorants, thixotropic agents, processing aids,nanoparticles, and fibers. In certain such embodiments, the additive ispresent in an amount of 0.01 to 10 wt. % relative to the mass of theliquid optically clear adhesive composition. In some exemplaryembodiments, the liquid optically clear adhesive composition furtherincludes metal oxide nanoparticles having a median particle diameter of1 nm to about 100 nm in an amount of 1 to 10 wt. %, relative to thetotal weight of the liquid optically clear adhesive composition.

In general, the LOCA composition may comprise metal oxide particles, forexample, to modify the refractive index of the adhesive layer or theviscosity of the liquid adhesive composition (as described below). Metaloxide particles that are substantially transparent may be used. Forexample, a 1 mm thick disk of the metal oxide particles in an adhesivelayer may absorb less than about 15% of the light incident on the disk.

Examples of metal oxide particles include clay, Al₂O₃, ZrO₂, TiO₂, V₂O₅,ZnO, SnO₂, ZnS, SiO₂, and mixtures thereof, as well as othersufficiently transparent non-oxide ceramic materials. The metal oxideparticles can be surface treated to improve dispersibility in theadhesive layer and the composition from which the layer is coated.Examples of surface treatment chemistries include silanes, siloxanes,carboxylic acids, phosphonic acids, zirconates, titanates, and the like.Techniques for applying such surface treatment chemistries are known.Organic fillers such as cellulose, castor-oil wax andpolyamide-containing fillers may also be used.

In some exemplary embodiments, LOCA compositions can be made thixotropicby adding particles to the compositions. In some embodiments, fumedsilica is added to impart thixotropic properties to a liquid adhesive,in an amount of from about 2 to about 10 wt %, or from about 3.5 toabout 7 wt %.

In some embodiments, the LOCA composition comprises a fumed silica.Suitable fumed silicas include, but are not limited to: AEROSIL 200; andAEROSIL R805 (both available from Evonik Industries); CAB-O-SIL TS 610;and CAB-O-SIL T 5720 (both available from Cabot Corp.), and HDK H2ORH(available from Wacker Chemie AG).

In some embodiments, the LOCA composition comprises a fumed aluminumoxide, such as AEROXIDE ALU 130 (available from Evonik, Parsippany,N.J.).

In some embodiments, the LOCA composition comprises clay such asGARAMITE 1958 (available from Southern Clay Products).

Metal oxide particles may be used in an amount needed to produce thedesired effect, for example, in an amount of from about 2 to about 10wt. %, from about 3.5 to about 7 wt. %, from about 10 to about 85 wt. %,or from about 40 to about 85 wt. %, based on the total weight of theadhesive layer. Metal oxide particles may only be added to the extentthat they do not add undesirable color, haze or transmissioncharacteristics. Generally, the particles can have an average particlesize of from about 1 nm to about 100 nm.

In some embodiments, the LOCA composition comprises nonreactiveoligomeric rheology modifiers. While not wishing to be bound by theory,non reactive oligomeric rheology modifiers build viscosity at low shearrates through hydrogen bonding or other self-associating mechanisms.Examples of suitable nonreactive oligomeric rheology modifiers include,but are not limited to: polyhydroxycarboxylic acid amides (such as BYK405, available from Byk-Chemie GmbH, Wesel, Germany),polyhydroxycarboxylic acid esters (such as BYK R-606, available fromByk-Chemie GmbH, Wesel, Germany), modified ureas (such as DISPARLON6100, DISPARLON 6200 or DISPARLON 6500 from King Industries,

Norwalk, Conn. or BYK 410 from Byk-Chemie GmbH, Wesel, Germany), metalsulfonates (such as K-STAY 501 from King Industries, Norwalk, Conn. orIRCOGEL 903 from Lubrizol Advanced Materials, Cleveland, Ohio),acrylated oligoamines (such as GENOMER 5275 from Rahn USA Corp, Aurora,Ill.), polyacrylic acids (such as CARBOPOL 1620 from Lubrizol AdvancedMaterials, Cleveland, Ohio), modified urethanes (such as K-STAY 740 fromKing Industries, Norwalk, Conn.), or polyamides.

In some embodiments, non-reactive oligomeric rheology modifiers arechosen to be miscible and compatible with the optically clear adhesiveto limit phase separation and minimize haze.

Photoinitiators may be used in the liquid compositions when curing withUV radiation. Photoinitiators for free radical curing include organicperoxides, azo compounds, quinines, nitro compounds, acyl halides,hydrazones, mercapto compounds, pyrylium compounds, imidazoles,chlorotriazines, benzoin, benzoin alkyl ethers, ketones, phenones, andthe like. For example, the adhesive compositions may compriseethyl-2,4,6-trimethylbenzoylphenylphosphinate available as LUCIRIN TPOLfrom BASF Corp. or 1-hydroxycyclohexyl phenyl ketone available asIRGACURE 184 from Ciba Specialty Chemicals. The photoinitiator is oftenused at a concentration of about 0.1 to 10 weight percent or 0.1 to 5weight percent based on the weight of oligomeric and monomer material inthe polymerizable composition.

The liquid compositions and adhesive layers can optionally include oneor more additives such as chain transfer agents, antioxidants,stabilizers, fire retardants, viscosity modifying agents, antifoamingagents, antistatic agents and wetting agents. If color is required forthe optical adhesive, colorants such as dyes and pigments, fluorescentdyes and pigments, phosphorescent dyes and pigments can be used.

Exemplary Substrates

Many of the contemplated embodiments of the present process involveformation of a patch of liquid optically clear conductive adhesive on arigid sheet or rigid article, e.g. the cover glass for an opticaldisplay or a liquid crystal display (LCD) module. However, somecontemplated embodiments involve formation of a patch of liquidoptically clear conductive adhesive on a transparent flexible sheet or atransparent flexible web of indefinite length in a roll-to-roll process.Flexible substrates may include flexible glass sheets or webs. Adiscussion of how flexible glass sheets or webs may be successfullyhandled in these sorts of embodiments can be found in U.S. PatentApplication Pub. No. 2013/0196163.

Thus, in additional exemplary embodiments, the substrate is a lightemitting display component or a light reflecting device component. Insome exemplary embodiments, the substrate is substantially transparent.In certain exemplary embodiments, the substrate is comprised of glass.In some particular embodiments, the substrate is flexible.

In additional exemplary embodiments, the substrate is a polymeric sheetor web. Suitable polymeric materials include, for example, polyesterssuch as polyethylene terephthalate (PET), polylactic acid (PLA) andpolyethylene naphthalate (PEN); polyimides such as KAPTON (availablefrom DuPont deNemours Corp., Wilmington, Del.); polycarbonates such asLEXAN (available from SABIC Innovative Plastics, Pittsfield, Mass.);cyclo olefin polymers such as ZEONEX or ZEONOR (available from ZeonChemicals LP, Louisville, Ky.); and the like.

Exemplary Coating Apparatus

Various exemplary embodiments of the disclosure will now be describedwith particular reference to the Drawings.

Referring now to FIG. 1, an exemplary coating apparatus 50 isillustrated. The apparatus 50 includes a support 52 for the substrate 22a on which the patch 24 is to be dispensed. Support 52 is moved by anactuator 54 (conveniently a zero-backlash actuator) during the coatingof the patch 24. Actuator 54 (among other things) is controlled bycontroller 60 via signal line 62. In some convenient embodiments, theactuator 54 may have an encoder that reports back to controller 60; inother convenient embodiments, a separate encoder may be provided forthis purpose. While the support 52 in the illustrated embodiment isflat, if the substrate 22 a is flexible or arcuate, a cylindricalsupport moved by a rotational actuator is considered within the scope ofthe disclosure. Positioned adjacent to the support 52 is a coating head70, which in the illustrated embodiment is a slot die. The coating head70 has an external opening 72, which in the convenient illustratedembodiment is a slot. The coating head 70 is moveably mounted so thatthe distance from its external opening 72 from the surface of thesubstrate 22 a can be controlled by linear actuator 74, which is in turncontrolled by controller 60 via signal line 76. (Coating head 70 isshown in partial cutaway to reveal certain internal structures) At leastone position sensor 78 is positioned so as to sense the distance betweenthe external opening 72 from the surface of the substrate 22 a, and itreports this information to controller 60 via signal line 80.

The coating head 70 conveniently has a cavity 82 which receives coatingliquid from syringe pump 90 via line 92 and delivers fluid to externalopening 72. The plunger 94 of syringe 90 is moved by actuator 96. Asensor 98 may be positioned so as to sense the exact position of theplunger 94 provides feedback via line 100 to controller 60 andindirectly to actuator 96 via signal line 102. Controller 60 provides asignal to the actuator 96 based on the input of sensor 98 and accordingto an equation discussed below which preferably takes into account notonly the position function, but also its first, second, and thirdderivatives. The bandwidth of the sensor-controller-actuator system ispreferably high, e.g. 100 Hz.

In the illustrated embodiment, liquid optically clear adhesives can bedrawn from a reservoir 104 via fluid line 106. A valve 110 is under thecontrol of controller 60 via line 112 for the purpose of cycling thesystem when the syringe pump needs to be recharged.

In a presently preferred embodiment of the present disclosure in whichthe coating liquid is a LOCA, best results are generally achieved ifthere is low compliance within the syringe pump/fluid line/coating headsystem. Air bubbles anywhere within this zone form an undesirable sourceof compliance. Therefore, in some convenient embodiments, plunger 94includes a purge valve through which air bubbles can be purged from thesystem. In order to detect when inadvertent compliance has entered thesystem, pressure sensors, positioned at, e.g. 114 and 116, and reportingto controller 60 via signal lines 118 and 120 respectively may bepresent. Alternatively, the current drawn by actuator 96 can bemonitored in lieu of the monitoring the pressure. As a furtheralternative, the system can also verify proper purging by dynamicallymeasuring compliance. A low displacement, high frequency motion from thesyringe pump while monitoring pressure can detect unwanted compliance inthe system.

Improved coating can be achieved as described below when the exactpresent viscosity of the liquid optically clear adhesive is known.Therefore in some convenient embodiments, an orifice 122 is present, andpressure sensors 124 and 126 provide information on the pressure dropacross the predetermined static or variable orifice 122 via signal lines128 and 130 respectively, which information can be processed to takeviscosity into account. Adjustability of orifice 122 is sometimesdesirable when the apparatus is asked to handle a wide range aviscosities and flow rates. A display and/or input device 140 in theform of a microcomputer or the like may be present, connected to thecontroller via data lines, collectively 142.

The coating head is preferably mounted to a fixture that preventssagging of the coating head. The fixture also has precise positioning,particularly with respect to the z-axis, to enable control of the heightof the coating head relative to the substrate. In one embodiment, thez-axis position can be controlled to within about 0.002 inch (0.00508cm), particularly to within about 0.0001 inch (0.000254 cm), and moreparticularly to within about 0.00001 inch (0.0000254 cm).

In one embodiment, the rigid platform, and thus the substrate, movesrelative to the coating head during the coating process. In anotherembodiment, the substrate is fixed while the coating head moves relativeto the rigid platform during the coating process. At the end of thecoating process and up through lamination to another substrate, theheight and dimensional tolerance of the coated LOCA remain withincertain dimensional tolerances.

In additional exemplary embodiments of any of the foregoing, the coatinghead can be selected from the group consisting of a single slot die, amultiple slot die, a single orifice die, and a multiple orifice die. Incertain such embodiments, the coating head is a single slot die having asingle die slot, further wherein the external opening is comprised ofthe die slot. In some particular such embodiments, the geometry of thesingle slot die is selected from a sharp-lipped extrusion slot die, aslot fed knife die with a land, or a notched slot die.

Thus in one presently preferred embodiment, the coating head includes aslot die. Slot die printing and coating methods, which have been usedfor adhesive coating for web or film to make tape and film products orsurface coating, have been found to provide a suitable method forprinting liquid compositions onto a target substrate. Slot dies can beemployed to dispose liquid optically clear compositions, such asadhesives, accurately and quickly in precision lamination applicationsinvolving gap filling between display panel and a cover substrate, suchas applications involving the lamination of a glass panel onto a displaypanel in LCD displays, or the lamination of a touch sensitive panel ontoa display panel in touch-sensitive electronic devices.

An example of a slot die for dispensing a feed stream of a liquidcomposition is described in PCT International Pub. No. WO 2011/087983.Such a slot die can be used to dispense liquid optically clearcompositions onto a substrate.

Parameters such as slot height and/or length, conduit diameter, flowchannel widths may be selected to provide for a desired layer thicknessprofile. For example, the cross-sectional area of flow channels 50 and52 may be increased or decreased. It may be varied along its length toprovide a certain pressure gradient that, in turn, may affect the layerthickness profile of multilayer flow stream 32. In this manner, thedimensions of one or more of the flow defining sections may be designedto influence the layer thickness distribution of the flow streamgenerated via feedblock 16, e.g., based on a target layer thicknessprofile.

In one embodiment, the coating head includes a slot fed knife diecontaining a converging channel. The geometry of the die could be asharp lipped extrusion die or a slot fed knife with land on either orboth the upstream and downstream lips of the die. A converging channelis preferred to avoid down-web ribbing and other coating defects. (SeeCoating and Drying Defects: Troubleshooting Operating Problems, E. B.Gutoff, E. D. Cohen, G. I. Kheboian, (John Wiley and Sons, 2006) pgs131-137). Such coating defects could lead to mura and other noticeableoptical defects in the display assembly.

In any of the foregoing exemplary embodiments, the source of the firstcoating liquid comprises a pre-metered coating liquid delivery systemselected from a syringe pump, a dosing pump, a gear pump, a servo-drivenpositive displacement pump, a rod-driven positive displacement pump, ora combination thereof.

In some exemplary embodiments, the coating head is preferably built tohandle pressures to shear the LOCA into the desired viscosity range. TheLOCA dispensed through the coating head may optionally be pre-heated orheated in the coating head to lower the viscosity of the LOCA and aidthe coating process. In some exemplary embodiments, a vacuum box ispositioned adjacent to the leading lip of the die to ensure that air isnot entrapped between the LOCA and the substrate and to stabilize thecoating bead.

In one embodiment, the coating head is a knife-coater, in which a sharpedge is used to meter the fluid onto the substrate. The coatingthickness is generally determined by the gap between the knife and thesubstrate. The gap is preferably well-controlled and is controlled inone embodiment to within about 0.002 inch (0.00508 cm), particularly towithin about 0.0001 inch (0.000254 cm), and more particularly to withinabout 0.00001 inch (0.0000254 cm). An example of a knife-coater coatinghead includes, but is not limited to, a β COATER SNC-280 commerciallyavailable from Yasui-Seiki Co., Bloomington, Ind.

An appropriate liquid feed for the first coating fluid (or LOCA), isrequired. The liquid feed may include, but is not limited to: a syringe,needle die, hopper or a liquid dispensing manifold. The liquid feed isengaged to dispense enough of the first coating liquid or LOCA for aparticular thickness over the coating area on the substrate (potentiallythrough the use of a precision syringe pump).

In some particular exemplary embodiments of the foregoing, at least onepressure sensor communicating with the source of the first coatingliquid or LOCA is used to measure a delivery pressure of the firstcoating liquid or LOCA. The delivery pressure is used to control atleast one of the delivery rate of the first coating liquid to thesubstrate, or a quality characteristic of the patch.

Suitable quality characteristics include the thickness uniformity of thepatch, the positional accuracy and/or precision of the patch position onthe substrate relative to a target position (as described further in thenext section), the uniformity of the patch perimeter (e.g. the“squareness” of a patch having a square-shaped perimeter), thestraightness of an edge of the patch, the absence of coating defects(e.g. bubbles, voids, entrained foreign matter, surface irregularities,and the like), the quantity (e.g. by weight or volume) of the firstcoating liquid forming the patch, and the like.

Exemplary Coated Articles and Laminates

Referring now to FIG. 2A, a top view of a coated sheet 20 a, includingpiece of sheet material 22 a and a patch 24 of coated liquid disposedupon one of its major surfaces, is illustrated. In the illustratedembodiment, the patch 24 is not coated all the way to the margins 26 ofthe piece of sheet material 22 a, leaving uncoated margins 30, 32, 34,and 36 on all sides of the perimeter of the patch 24. In manyapplications where the coated patch 24 is to be used in, e.g. a liquidcrystal display for a hand-held device, it is convenient to have suchmargins. Further, it is often convenient for one or more of thesemargins 30, 32, 34, and 36 to have a pre-determined width, accurate to aclose tolerance.

In such applications, positional accuracy within 0.3 mm, or even 0.1 mmcan be achieved with the present disclosure. In further exemplaryembodiments of any of the foregoing, the perimeter of the patch isdefined by a plurality of lateral edges of the patch. In suchapplications, positional accuracy of the patch within +/−0.3 mm, or even+/−0.1 mm can be achieved with the present disclosure. In some suchembodiments, at least one lateral edge of the patch is positionedrelative to an edge of the substrate to within +/−1,000 μm, +/−750 μm+/−500 μm, +/−400 μm, +/−300 μm, or even within +/−200 μm or +/−100 μmof a target position.

However, the placement of patches when the size of the margin is notcritical, or even when the patches are coated all the way to one or moreof the margin edges 26, are considered to be within the scope of thedisclosure. In the illustrated embodiment, the patch has a substantiallyuniform thickness, but this is not considered a requirement of thedisclosure, as will be discussed with more particularity in connectionwith FIGS. 2C and 2D below.

In some exemplary embodiments, the LOCA is dispensed so as to generate apatch having a thickness of between about 1 μm and about 5 mm, moreparticularly of between about 50 μm and about 5 mm, even moreparticularly of between about 50 μm and about 1 mm, and still moreparticularly between about 50 μm and about 0.3 mm. In some exemplaryembodiments, the thickness over the entire coating region is within lessthan about 100 μm of a predetermined target coating thickness,particularly within less than about 50 μm of the target coatingthickness, more particularly within about 30 μm of the target coatingthickness, and still more particularly within about 5 μm of the targetcoating thickness.

In some exemplary embodiments, the substrate and the coating head moveat a speed of between about 0.1 mm/s and about 3000 mm/s relative to oneanother, particularly between about 1 mm/s and about 1000 mm/s relativeto one another, and more particularly between about 3 mm/s and about 500mm/s relative to one another.

Referring now to FIG. 2B, a top view of a section along the length of acoated web 20 b of indefinite length material, including the web 22 band a series of patches 24 of coated liquid disposed along it, isillustrated. In the illustrated embodiment, the patch 24 is not coatedall the way to the margins 26 of the piece of web 22 b, leaving uncoatedmargins 30, and 34 on the sides of the patch 24, and an uncoated space38 between one patch 24 and the next. In many applications where thecoated patch 24 is to be used in, e.g. a liquid crystal display for ahand-held device, it is convenient to have such margins. Further, it isoften convenient for one or more of these margins 30 and 34, anduncoated space 38 to have a pre-determined width, accurate to a closetolerance.

In such applications, positional accuracy within 0.3 mm, or even −0.1 mmcan be achieved with the present disclosure. In some such embodiments,at least one lateral edge of the patch is positioned relative to an edgeof the substrate to within +/−1,000 μm, +/−750 μm +/−500 μm, +/−400 μm,+/−300 μm, or even within +/−200 μm or +/−100 μm of a target position.

However, the placement of patches when the size of the margin is notcritical, or even when the patches are coated all the way to one or moreof the margin edges 26, are considered to be within the scope of thedisclosure.

Further, the illustrated embodiment includes fiducial marks 40 which canbe used to determine the position of the web 22 b with great accuracy inboth the machine direction and the cross-direction. A more completediscussion of the creation and interpretation of diverse fiducial markscan be found in U.S. Pat. No. 8,405,831 and U.S. Patent Application Pub.Nos. 2010/0188668, 2010/0196607, 2011/0247511, and 2011/0257779.

Referring now to FIG. 2C, a side view of a portion of a sheet ofsubstrate material 22 a having a patch of coated liquid 24′ disposed onone of its major surfaces, is illustrated. In this FIGURE, patch 24′ hasa thickness with a deliberately non-uniform side profile. The apparatusof FIG. 1 can produce such a patch by first gradually ramping up thepumping rate and gradually withdrawing the first coating head 70 as thesubstrate is translated to create the gentle curved slope up to thepeak, then gradually decreasing the pumping rate and advancing thecoating head 70 as the substrate is translated. The ordinary artisanwill perceive that with a sufficiently detailed programming thecontroller 60 can produce many profiles for various end uses as long asthey are within the bandwidth of the apparatus 50 and the viscositylimitations of the LOCA composition (the composition has a finiteEquilibrium Viscosity and cannot be expected to adopt the shape ofextremely small features). FIG. 2D is a top view of the coated sheet ofFIG. 2C. While patches that are as nearly rectilinear as possible aredesirable for some purposes, the techniques of the present disclosuremay be used to create profiled patches that are useful for otherpurposes. In particular, profiled patch 24′ may make the lamination of arigid cover layer easier.

Referring now to FIG. 2E, a side view of a portion of a sheet ofsubstrate material 22 a having a patch of coated liquid 24″ disposed onone of its major surfaces, is illustrated. In patch 24″ the coatedliquid has a thickness with a deliberately non-uniform side profile.FIG. 2F is a top view of the coated sheet of FIG. 2E. In this view alongitudinal stripe 180 has been created by having an exceptionally widespot in the slot of the slot die, while crosswise stripe 182 has beencreated by moving the slot away from the substrate 22 a briefly at theproper moment as the substrate 22 a is in motion. During this briefmoving away, the pumping rate needs to be increased appropriately todeliver the needed extra volume of LOCA.

Referring now to FIG. 2G, a side view of a portion of a sheet ofsubstrate material 22 a having a patch of coated liquid 24′″ disposed onone of its major surfaces, is illustrated. In patch 24′ coated liquidhas a thickness with a deliberately non-uniform side profile. In thisview a series of longitudinal ribs 200 has been created by having aseries of exceptionally wide spots in the slot of the slot die. This maybe referred to as a notched slot or a notched die. An alternative way ofachieving a similar surface conformation would be to contact a patchcreated by a straight slot die with a contacting tool post-coating. Forinstance, a wire wound rod can be manually pulled over the coating tocreate a ribbed structure.

Referring now to FIG. 2H, a top view of a coated sheet similar to thatof FIG. 2G, except that in addition to longitudinal ribs 200, acrosswise stripe 202 has been created by moving the slot away from thesubstrate 22 a briefly at the proper moment as the substrate 22 a is inmotion. Similarly to the discussion above in connection with FIG. 2F,during this brief moving away, the pumping rate needs to be increasedappropriately to deliver the needed extra volume of LOCA.

Referring now to FIG. 3, a photograph of a substrate with a recentlycoated patch thereon is illustrated. In this run, the slot die is beingraised from the substrate at the trailing edge of the patch relativelyquickly, such that coating bead is breaking a several different placesalong the cross direction. In this configuration the small breaks aretoo small to be undesirable in many applications.

Referring now to FIG. 4, a photograph of a substrate with a recentlycoated patch thereon is illustrated. Compared to the situation depictedin FIG. 3, the slot die is being raised from the substrate at thetrailing edge of the patch relatively slowly, such that coating bead isbreaking at a single point in the center of the trailing edge.Surprisingly, considering the configuration shown in FIG. 3, both arelatively quick and a relatively slow retraction of the slot dieproduce the best margins. Intermediate retraction rates between thesetwo desirable regimes produce less desirable trailing edges.

Referring now to FIG. 5, a photograph of a substrate with a recentlycoated patch thereon having undesirable margin on the leading edge ispresented. A margin like this has been found to result from due tocompressibility in the fluid system.

Referring now to FIG. 6, a photograph of a substrate with a recentlycoated patch thereon having undesirable margin on the leading edge ofone patch and the trailing edge of an adjacent patch is presented. Amargin with this type of irregularity has typically been found to be dueto a bubble in the die cavity.

In any of the foregoing exemplary embodiments, the patch may cover onlya portion of a first major surface of the substrate. In some exemplaryembodiments, the perimeter exhibits a geometric shape selected from asquare, a rectangle, or a parallelogram. In certain exemplaryembodiments, the predetermined position is selected such that theperimeter of the patch has a center proximate a center of the majorsurface of the substrate.

In further exemplary embodiments of any of the foregoing, the thicknessof the patch is non-uniform. In some such embodiments, the thickness ofthe patch is greater proximate the center of the patch, and thethickness of the patch is lower proximate the perimeter of the patch. Incertain embodiments, the patch includes at least one raised discreteprotrusion extending outwardly from the major surface of the substrate.In further such exemplary embodiments, the at least one raised discreteprotrusion is comprised of at least one raised rib extending across atleast a portion of the major surface of the substrate. In some suchembodiments, the at least one raised rib includes at least two raisedribs arranged cross-wise on the major surface of the substrate. Incertain such embodiments, the at least two ribs intersect and overlapproximate the center of the perimeter of the patch.

In other exemplary embodiments, the at least one raised discreteprotrusion is a multiplicity of raised discrete protrusions. In somesuch exemplary embodiments, the multiplicity of raised discreteprotrusions is selected from a plurality of raised discrete bumps, amultiplicity of raised discrete ribs, or a combination thereof. Incertain such embodiments, the multiplicity of raised discrete bumps iscomprised of hemispherically-shaped bumps. Optionally, the multiplicityof raised discrete bumps is arranged in an array pattern. In someparticular embodiments, the multiplicity of raised discrete ribs form adogbone-shaped pattern. sec⁻¹ In other exemplary embodiments, themultiplicity of raised discrete ribs is comprised of elliptically-shapedribs. In some such embodiments, the multiplicity of raised discrete ribsis arranged such that each rib is arranged substantially parallel toeach adjoining rib. In certain such embodiments, at least two of themultiplicity of raised discrete ribs are arranged substantially parallelto each other, and at least one of the multiplicity of raised discreteribs is arranged substantially orthogonal to the at least twosubstantially parallel raised discrete ribs.

In alternative exemplary embodiments to those described in the precedingtwo paragraphs, the thickness of the patch is substantially uniform.Optionally, a mean thickness of the patch is from about 1 μm to about500 μm. In some such exemplary embodiments, the thickness of the patchhas a uniformity of +/−10% of the mean thickness or better.

In further exemplary embodiments of any of the foregoing, the perimeterof the patch is defined by a plurality of lateral edges of the patch. Insome such embodiments, at least one lateral edge of the patch ispositioned relative to an edge of the substrate to within +/−500 μm of atarget position.

Exemplary Lamination Processes

The operation of exemplary embodiments of the present disclosure will befurther described with regard to the following non-limiting detailedExamples. These examples are offered to further illustrate the variousspecific and preferred embodiments and techniques. It should beunderstood, however, that many variations and modifications may be madewhile remaining within the scope of the present disclosure.

In further exemplary embodiments of any of the foregoing coatingprocesses, the process includes a lamination step including disposing asecond substrate relative to the first substrate such that the patch ispositioned between the first and second substrates, wherein the patchcontacts at least a portion of each of the first and second substrates,thereby forming a laminate. The lamination process may be advantageouslyused to make optical assemblies such as display panels.

Optical materials may be used to fill gaps between optical components orsubstrates of optical assemblies. Optical assemblies comprising adisplay panel bonded to an optical substrate may benefit if the gapbetween the two is filled with an optical material that matches ornearly matches the refractive indices of the panel and the substrate.For example, sunlight and ambient light reflection inherent between adisplay panel and an outer cover sheet may be reduced. Color gamut andcontrast of the display panel can be improved under ambient conditions.Optical assemblies having a filled gap can also exhibit improvedshock-resistance compared to the same assemblies having an air gap.

Optical materials used to fill gaps between optical components orsubstrates typically comprise adhesives and various types of curedpolymeric compositions. However, these optical materials are not usefulfor making an optical assembly if, at a later time, one wishes todisassemble or rework the assembly with little or no damage to thecomponents. This reworkability feature is needed for optical assembliesbecause the components tend to be fragile and expensive. For example, acover sheet often needs to be removed from a display panel if flaws areobserved during or after assembly or if the cover sheet is damaged aftersale. It is desirable to rework the assembly by removing the cover sheetfrom the display panel with little or no damage to the components.Reworkability is becoming increasingly important as the size or area ofavailable display panels continues to increase.

Optical Assemblies

An optical assembly having a large size or area can be difficult tomanufacture, especially if efficiency and stringent optical quality aredesired. A gap between optical components may be filled by pouring orinjecting a curable composition into the gap followed by curing thecomposition to bond the components together. However, these commonlyused compositions have long flow-out times which contribute toinefficient manufacturing methods for large optical assemblies.

The optical assembly disclosed herein comprises an adhesive layer andoptical components, particularly a display panel and a substantiallylight transmissive substrate. The adhesive layer allows one to reworkthe assembly with little or no damage to the components. Optionally, theadhesive layer may have a cleavage strength between glass substrates ofabout 15 N/mm or less, 10 N/mm or less, or 6 N/mm or less, such thatreworkability can be obtained with little or no damage to thecomponents. Total energy to cleavage can be less than about 25 kg-mmover a 1 by 1 inch (2.54 by 2.54 cm) area.

Substantially Transparent Substrates

The substantially transparent substrate used in the optical assembly maycomprise a variety of types and materials. The substantially transparentsubstrate is suitable for optical applications and typically has atleast 85% transmission of visible light over the range of from 460 to720 nm. The substantially transparent substrate may have, per millimeterthickness, a transmission of greater than about 85% at 460 nm, greaterthan about 90% at 530 nm, and greater than about 90% at 670 nm.

The substantially transparent substrate may comprise glass or polymer.Useful glasses include borosilicate, soda lime, and other glassessuitable for use in display applications as protective covers. Oneparticular glass that may be used comprises EAGLE XG and JADE glasssubstrates available from Corning Inc. Useful polymers include polyesterfilms such as polyethylene terephalate, polycarbonate films or plates,acrylic films such as polymethylmethacrylate films, and cycloolefinpolymer films such as ZEONOX and ZEONOR available from Zeon ChemicalsL.P. The substantially transparent substrate preferably has an index ofrefraction close to that of display panel and/or the adhesive layer; forexample, from about 1.4 and about 1.7. The substantially transparentsubstrate typically has a thickness of from about 0.5 to about 5 mm.

The substantially transparent substrate may comprise a touch screen.Touch screens are well known and generally comprise a transparentconductive layer disposed between two substantially transparentsubstrates. For example, a touch screen may comprise indium tin oxidedisposed between a glass substrate and a polymer substrate.

Adhesive Layers

The adhesive layer is preferably suitable for optical applications. Forexample, the adhesive layer may have at least 85% transmission over therange of from 460 to 720 nm. The adhesive layer may have, per millimeterthickness, a transmission of greater than about 85% at 460 nm, greaterthan about 90% at 530 nm, and greater than about 90% at 670 nm. Thesetransmission characteristics provide for uniform transmission of lightacross the visible region of the electromagnetic spectrum which isimportant to maintain the color point in full color displays.

The color portion of the transparency characteristics of the adhesivelayer is further defined by its color coordinates as represented by theCIE L*a*b* convention. For example, the b* component of color should beless than about 1, more preferably less than about 0.5. Thesecharacteristics of b* provide for a low yellowness index which isimportant to maintain the color point in full color displays.

The haze portion of the transparency characteristics of the adhesivelayer is further defined by the % haze value of the adhesive layer asmeasured by haze meters such as a HazeGard Plus available from BykGardner or an UltraScan Pro available from Hunter Labs. The opticallyclear article preferably has haze of the of less than about 5%,preferably less than about 2%, most preferably less than about 1%. Thesehaze characteristics provide for low light scattering which is importantto maintain the quality of the output in full color displays.

For reasons described above, the adhesive layer preferably has arefractive index that matches or closely matches that of the displaypanel and/or the substantially transparent substrate. The refractiveindex of the adhesive can be controlled by the proper choice of adhesivecomponents. For example, the refractive index can be increased byincorporating oligomers, diluting monomers and the like which contain ahigher content of aromatic structure or incorporate sulfur or halogenssuch as bromine. Conversely the refractive index can be adjusted tolower values by incorporating oligomer, diluting monomers and the likethat contain a higher content of aliphatic structure. For example, theadhesive layer may have a refractive index of from about 1.4 to about1.7.

The adhesive may remain transparent by the proper choice of adhesivecomponents including oligomers, diluting monomers, fillers,plasticizers, tackifying resins, photoinitiators and any other componentwhich contributes to the overall properties of the adhesive. Inparticular, the adhesive components should be compatible with eachother, for example they should not phase separate before or after cureto the point where domain size and refractive index differences causelight scattering and haze to develop, unless haze is a desired outcome,such as for diffuse adhesive applications. In addition the adhesivecomponents should be free of particles that do not dissolve in theadhesive formulation and are large enough to scatter light, and therebycontribute to haze. If haze is desired, such as in diffuse adhesiveapplications, this may be acceptable. In addition, various fillers suchas thixotropic materials should be so well dispersed that they do notcontribute to phase separation or light scattering which can contributeto a loss of light transmission and an increase in haze. Again, if hazeis desired, such as in diffuse adhesive applications, this may beacceptable. These adhesive components also should not degrade the colorcharacteristics of transparency by, for example, imparting color orincreasing the b* or yellowness index of the adhesive layer.

The adhesive layer (i.e. the patch of the first coating liquid or LOCAcoated on the substrate) can be used in an optical assembly including adisplay panel, a substantially transparent substrate, and the adhesivelayer disposed between the display panel and the substantiallytransparent substrate.

The adhesive layer may have any thickness. The particular thicknessemployed in the optical assembly may be determined by any number offactors, for example, the design of the optical device in which theoptical assembly is used may require a certain gap between the displaypanel and the substantially transparent substrate. The adhesive layertypically has a thickness of from about 1 μm to about 5 mm, from about50 μm to about 1 mm, or from about 50 μm to about 0.2 mm.

The optical assembly may be prepared using an assembly fixture such asthe one described in U.S. Pat. No. 5,867,241. In this method, a fixturecomprising a flat plate with pins pressed into the flat plate isprovided. The pins are positioned in a predetermined configuration toproduce a pin field which corresponds to the dimensions of the displaypanel and of the component to be attached to the display panel. The pinsare arranged such that when the display panel and the other componentsare lowered down into the pin field, each of the four corners of thedisplay panel and other components is held in place by the pins. Thefixture aids assembly and alignment of the components of an opticalassembly with suitable control of alignment tolerances. Additionalembodiments of this assembly method are described in U.S. Pat. No.6,388,724 B1, describes how standoffs, shims, and/or spacers may be usedto hold components at a fixed distance to each other.

Curing

In some embodiments, the process further includes curing the coatingliquid by applying heat, actinic radiation, ionizing radiation, or acombination thereof.

Any form of electromagnetic radiation may be used, for example, theliquid compositions may be cured using UV-radiation and/or heat.Electron beam radiation may also be used. The liquid compositionsdescribed above are said to be cured using actinic radiation, i.e.,radiation that leads to the production of photochemical activity. Forexample, actinic radiation may comprise radiation of from about 250 toabout 700 nm. Sources of actinic radiation include tungsten halogenlamps, xenon and mercury arc lamps, incandescent lamps, germicidallamps, fluorescent lamps, lasers and light emitting diodes. UV-radiationcan be supplied using a high intensity continuously emitting system suchas those available from Fusion UV Systems.

In some embodiments, actinic radiation may be applied to a layer of theliquid composition such that the composition is partially polymerized.The liquid composition may be disposed between the display panel and thesubstantially transparent substrate and then partially polymerized. Theliquid composition may be disposed on the display panel or thesubstantially transparent substrate and partially polymerized, then theother of the display panel and the substrate may be disposed on thepartially polymerized layer.

In some embodiments, actinic radiation may be applied to all or aportion of a layer of the liquid composition such that the compositionis completely or nearly completely polymerized in at least theirradiated region. The liquid composition may be disposed between thedisplay panel and the substantially transparent substrate and thencompletely or nearly completely polymerized. The liquid composition maybe disposed on the display panel or the substantially transparentsubstrate and completely or nearly completely polymerized, than theother of the display panel and the substrate may be disposed on thepolymerized layer.

In the assembly process, it is generally desirable to have a layer ofthe liquid composition that is substantially uniform. Radiation may thenbe applied to form the adhesive layer.

Display Panels

In some particular exemplary embodiments, the laminate is comprised of adisplay panel selected from an organic light-emitting diode display, anorganic light-emitting transistor display, a liquid crystal display, aplasma display, a surface-conduction electron-emitter display, a fieldemission display, a quantum dot display, a liquid crystal display, amicro-electromechanical system display, a ferro liquid display, athick-film dielectric electroluminescent display, a telescopic pixeldisplay, or a laser phosphor display.

The display panel may comprise any type of panel such as a liquidcrystal display panel. Liquid crystal display panels are well known andtypically comprise a liquid crystal material disposed between twosubstantially transparent substrates such as glass or polymersubstrates. As used herein, substantially transparent refers to asubstrate that is suitable for optical applications, e.g., has at least85% transmission over the range of from 460 to 720 nm. Opticalsubstrates may have, per millimeter thickness, a transmission of greaterthan about 85% at 460 nm, greater than about 90% at 530 nm, and greaterthan about 90% at 670 nm. On the inner surfaces of the substantiallytransparent substrates are transparent electrically conductive materialsthat function as electrodes. In some cases, on the outer surfaces of thesubstantially transparent substrates are polarizing films that passessentially only one polarization state of light. When a voltage isapplied selectively across the electrodes, the liquid crystal materialreorients to modify the polarization state of light, such that an imageis created. The liquid crystal display panel may also comprise a liquidcrystal material disposed between a thin film transistor array panelhaving a plurality of thin film transistors arranged in a matrix patternand a common electrode panel having a common electrode.

The display panel may comprise a plasma display panel. Plasma displaypanels are well known and typically comprise an inert mixture of noblegases such as neon and xenon disposed in tiny cells located between twoglass panels. Control circuitry charges electrodes within the panelwhich causes the gases to ionize and form a plasma, which then excitesphosphors to emit light.

The display panel may comprise an organic electroluminescence panel.These panels are essentially a layer of an organic material disposedbetween two glass panels. The organic material may comprise an organiclight emitting diode (OLED) or a polymer light emitting diode (PLED).These panels are well known.

The display panel may comprise an electrophoretic display.Electrophoretic displays are well known and are typically used indisplay technology referred to as electronic paper or e-paper.Electrophoretic displays comprise a liquid charged material disposedbetween two transparent electrode panels. Liquid charged material maycomprise nanoparticles, dyes and charge agents suspended in a nonpolarhydrocarbon, or microcapsules filled with electrically charged particlessuspended in a hydrocarbon material. The microcapsules may also besuspended in a layer of liquid polymer.

The optical assemblies and/or display panels disclosed herein may beused in a variety of optical devices including, but not limited to, ahandheld device such as a phone, a television, a computer monitor, aprojector, a sign. The optical device may comprise a backlight.

EXAMPLES

These Examples are merely for illustrative purposes and are not meant tobe overly limiting on the scope of the appended claims. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof the present disclosure are approximations, the numerical values setforth in the specific examples are reported as precisely as possible.Any numerical value, however, inherently contains certain errorsnecessarily resulting from the standard deviation found in theirrespective testing measurements. At the very least, and not as anattempt to limit the application of the doctrine of equivalents to thescope of the claims, each numerical parameter should at least beconstrued in light of the number of reported significant digits and byapplying ordinary rounding techniques.

Summary of Materials

All parts, percentages, ratios, and the like in the Examples and therest of the specification are by weight, unless noted otherwise.Solvents and other reagents used may be obtained from Sigma-AldrichChemical Company (Milwaukee, Wis.) unless otherwise noted.

Test Methods

Viscosity Measurement

Viscosity measurements were made by using an AR2000 Rheometer equippedwith a 40 mm, 1° stainless steel cone and plate from TA Instruments, NewCastle, Del. Viscosities were measured at 25° C. using a steady stateflow procedure at several shear rates from 0.01 to 100 sec⁻¹ with a 28μm gap between cone and plate.

Experimental Apparatus

A first coating apparatus was constructed as generally depicted inFIG. 1. A substrate support 52 was mounted on precision sliding bearingscommercially available as model SHS-15 from THK Co. (Tokyo, JP), and wasmoved by an actuator commercially available as model ICD10-100A1 linearmotor from Kollmorgen (Radford, Va.), provided with a drive/amplifiercommercially available as model AKD-P00306-NAEC-0000, also fromKollmorgen. Mounted above the substrate support was a coating head inthe form of a slot die having a cavity and being of conventional type, 4inches (102 mm) wide. The coating head was mounted on a linear actuatorcommercially available as model ICD 10-100 from Kollmorgen. An encoderintegral to the linear actuator was used to monitor the die gap betweenthe slot from the surface of the substrate in cooperation with aphysical standard (a precision shim). It is contemplated that otherposition sensors, such as laser triangulation sensors, could beadditionally employed, especially when the flatness of the substrate isan issue. It has been found in practice that the actuator, sensor,physical geometry of the components and the stiffness of the mechanicalsystem all play a role in the ability to achieve both a high dimensionalaccuracy of the patch and the cleanness of the leading and trailingedges.

A 100 ml stainless steel syringe 90, commercially available as model702261 from Harvard Precision Instruments, Inc. (Holliston, Mass.), wasused to dispense fluid into fluid line 92. The actuator 96 was as modelICD10-100A1 linear motor from Kollmorgen, provided with adrive/amplifier commercially available as model AKD-P00306-NAEC-0000,also from Kollmorgen. The sensor 98 was a read head commerciallyavailable as RGH20 L-9517-9125 with a 20 micron tape scale fromRenishaw, Inc. (Hoffman Estates, IL). The several pressure transducersdescribed above were commercially available as 280E (100 psig range; 689kPa) from Setra Systems, Inc. (Boxborough, Mass.). Controller 60 wasavailable as CX1030, equipped with a point to point motion profile, fromBeckhoff Automation LLC (Burnsville, Minn.).

In the several Examples below, motion profiles executed by thecontroller were used in two manners to achieve precise patch coating.The first manner was to use position profiles to determine the finalshape of the patch that is applied. The profiles were initially createdby using volumetric calculations and physical models to determine theapproximate material flow rate and position at each instant of time. Theintegral of the flow rate, over the die position relative to thesubstrates, determines the coated surface's profile. In addition, aprofile is entered for positioning the die relative to the surface, aswell as the substrate position and velocity relative to the die.

Next, multiple coatings were applied, and the actual achieved profilewas measured. Because of higher order physical affects, there were somedifferences between the predicted edge start position, ending position,and profile and the actual outcome. By iteratively adjusting the motionprofile, these differences from the desired profile were attenuated oreliminated. For example, if the patch starting edge is 100 microns late(perhaps because the instant model had some errors from the actual modelof the geometry of the pump, die and delivery system, including fluiddynamics), the starting profile may be advanced by a velocity integratedover time to equal to 100 microns. Similarly, if the starting edge isnot sharp enough, an initial step can be introduced to provideadditional fluid at the start, increasing edge sharpness.

The second manner in which the profiles were used was to manage theposition, velocity, acceleration, and jerk rate (or more specificallythe position vs. time equation and its first three derivatives). As afor example, one might suppose that a good leading or trailing edgecould be achieved simply by asking the apparatus to provide as close toan infinitely sharp step as possible. However, experience has shown thatseveral problems occur. One is if the actual profile is not within thecontrollers capability (due to physical constraints), then differencesfrom the planned path and the actual path occur. This resulted in coatedprofile error.

The second aspect is that when high forces are applied to the mechanics,mechanical deflections of the position of the die and pump occur. Thiscauses additional errors. In addition, these defections store energy,which result in a “ringing” of the mechanical components, this causesapplied profile errors long after the initial impulse has occurred. Bylimiting the derivatives to achievable values, and blending motionsegments by keeping the derivatives as continuous as possible acrosssegment boundaries, much higher accuracy was achieved. While motionprofiles per se are known in precision motion control, the use of higherderivations is not presently done in connection with precision coating.In addition, no motion profile segments are known in the context ofcompensating for an undesired coated surface profile.

Further, exemplary embodiments of the present disclosure also coordinatethe motion of the substrate relative to the die to further enhance theaccuracy of the coated patch. For example, suppose it is desirable toapproximate an infinitely sharp start of the application of the coatingliquid to the substrate (e.g. the thickness of the patch goes from athickness of 0 microns to a thickness of 300 microns over a relativemovement of the die slot and the substrate of zero microns. However, wecan dramatically improve upon the positional accuracy by coordinatingthe profile of the die, pump, and substrate.

Thus, instead of high acceleration motions, we can slowly ramp up allthree profiles, so the initial contact of the coating bead to thesubstrate is at a very slow velocity (near or potentially zero). Then wecan ramp up the substrate position in lock step with the pump to deliveran extremely sharp edge. Note also that since high accelerations are notintroduced into the system, the profile may be positioned on thesubstrate with high accuracy.

Example 1

An alternate apparatus was also built, generally similar to theapparatus depicted in FIG. 1, and discussed above, except that thesupport for the substrate was cylindrical and was put into rotary motionin order to create relative motion between the coating head and thesubstrate. More specifically, the support was an aluminum drum, 32.4 cmin diameter, whose rotational motion was controlled by a motor,commercially available as model FH5732 from Kollmorgen, coupled to thedrum by air bearings commercially available as BLOCK-HEAD 10R fromProfessional Instruments of Hopkins, Minn.

The drum was cleaned with isopropyl alcohol and allowed to dry. Severalsheets of 0.1 mm thick by 300 mm long by 150 mm wide flexible glasscommercially available as OA10G from Nippon Electric Glass America, Incof Schaumburg, Ill. were adhered to the drum. A pseudoplastic andthixotropic liquid optically clear adhesive, commercially available as1033 STENCIL PRINTABLE OPTICALLY CLEAR ADHESIVE from 3M Company of St.Paul, Minn. was prepared. This LOCA was tested for viscosity accordingto the test method above and found to be 702 Pa-sec at a shear rate of0.01 sec⁻¹, 182.8 Pa-sec at a shear rate of 0.1 sec⁻¹, 39.5 Pa-sec at ashear rate of 1 sec⁻¹, 15.6 Pa-sec at a shear rate of 10 sec⁻¹, and 10.1Pa-sec at a shear rate of 100 sec⁻¹.

The LOCA was fed into the empty syringe from the remote reservoir usinga pressure of 80 psi (552 kPa). During filling, a vent at the top of theplunger body was open, enabling trapped air escape. This vent was closedonce bubble-free resin was flowing from it. The filling continued untilbubble-free resin was flowing from the die slot, then a valve betweenthe coating system (syringe and die) and the remote reservoir wasclosed. The gap between the die slot and the aluminum drum was verifiedand the die slot was positioned at its starting gap using a precisionshim. The syringe pump fed into a coating head in the form of a slot diehaving a 4 inch (10.2 cm) wide by 0.020 inch (0.51 mm) high slot with a0.001 inch (0.025 mm) overbite.

The controller was programmed to simultaneously control the variousactuators in terms of several distinct time segments of not necessarilyequal length. These parameters are summarized in Table 1. Of course, theordinary artisan will perceive that the programming could be performedin terms of any of several other convenient parameters, such as thedistance of longitudinal travel of the substrate. This last might beparticularly convenient in terms of a web of indefinite length,particularly a web of indefinite length having fiducial marks asillustrated in FIG. 2B.

Eight patches were coated, two per glass sheet, around the circumferenceof the aluminum drum with small gaps in-between each patch and the next.A position and thickness sensor, commercially available as model LT-9010M, from Keyence America of Itasca, Ill. was scanned across the coatedpatches to verify thickness uniformity.

TABLE 1 Velocity of Velocity Movement of Cumulative Distance of the SlotMovement Time Duration Time at Translation From Die to the of theSegment of the End of Speed of Slot to Specified Syringe (arbitrarySegment Segment Substrate Substrate Distance Plunger units (sec) (sec)(rpm) (mm) (mm/sec) (mm/sec) 0 0.223 0.223 1.498 3.00 15 0.000 1 0.1380.360 1.498 0.200 15 3.000 2 3.867 4.228 1.498 0.200 15 0.548 3 0.1704.398 1.498 0.200 15 −3.000 4 10.000* 5.398 0.0912 3.00 15 0.000 *Thissegment is provided to space one patch from an adjacent patch around thedrum.

Example 2

The set-up for this Example is generally similar to that of Example 1,except for the programming provided to the controller. Table 2summarizes this Example.

TABLE 2 Velocity of Velocity Movement of Cumulative Distance of the SlotMovement Time Duration Time at Translation From Die to the of theSegment of the End of Speed of Slot to Specified Syringe (arbitrarySegment Segment Substrate Substrate Distance Plunger units (sec) (sec)(rpm) (mm) (mm/sec) (mm/sec) 0 0.223 0.223 1.498 3.00 15 0.000 1 0.1650.388 1.498 0.200 15 2.000 2 3.840 4.228 1.498 0.200 15 0.548 3 0.2044.432 1.498 0.200 15 −2.000 4 10.000* 14.432 0.086 3.00 15 0.000 *Thissegment is provided to space one patch from an adjacent patch around thedrum.

Example 3

The sample according to Example 1 was carefully removed from the drumand placed on a granite table. A similarly sized sheet of EAGLE XGdisplay glass, commercially available for Corning, of Corning N.Y., wasmanually laminated using motion normal to the surface of the granite andin normal atmosphere. A slight curvature was forced of the display glassduring lamination to reduce the resulting pockets of trapped gas duringlamination. The resulting sample showed pockets of trapped gas, thoughit is anticipated that lamination in vacuum or lamination with machinemanipulation of the display glass would produce better results.

Example 4

The procedure of Example 1 is repeated, except that the flow parametersare modified to produce the patch illustrated in FIGS. 2C and 2D. Alamination of display glass generally as described in Example 3 isperformed. A lamination without trapped gas bubbles is observed.

Example 5

The sample according to Example 1 is carefully removed from the drum andplaced on a granite table. A wire wound rod commercially available as a#75 Mayer Rod, from R.D. Specialties of Webster, N.Y., is manuallypulled over the coating to create a ribbed structure with the ribs' longaxis parallel to the direction of subsequent lamination. A similarlysized sheet of EAGLE XG display glass is laminated using motion normalto the surface of the granite and in normal atmosphere.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment,” whether ornot including the term “exemplary” preceding the term “embodiment,”means that a particular feature, structure, material, or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the certain exemplary embodiments of the presentdisclosure. Thus the appearances of the phrases such as “in one or moreembodiments,” “in certain embodiments,” “in one embodiment” or “in anembodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the certain exemplaryembodiments of the present disclosure. Furthermore, the particularfeatures, structures, materials, or characteristics may be combined inany suitable manner in one or more embodiments.

While the specification has described in detail certain exemplaryembodiments, it will be appreciated that those skilled in the art, uponattaining an understanding of the foregoing, may readily conceive ofalterations to, variations of, and equivalents to these embodiments.Accordingly, it should be understood that this present disclosure is notto be unduly limited to the illustrative embodiments set forthhereinabove. Furthermore, all publications, published patentapplications and issued patents referenced in the Detailed Descriptionare incorporated herein by reference in their entirety to the sameextent as if each individual publication or patent was specifically andindividually indicated to be incorporated by reference. Variousexemplary embodiments have been described. These and other embodimentsare within the scope of the following claims.

1. A process, comprising: providing a coating head, the coating headcomprising an external opening in flow communication with a source of afirst coating liquid; positioning the coating head relative to asubstrate to define a gap between the external opening and thesubstrate; creating relative motion between the coating head and thesubstrate in a coating direction; and dispensing a pre-determinedquantity of the first coating liquid from the external opening onto atleast a portion of at least one major surface of the substrate to form adiscrete patch of the first coating liquid in a predetermined positionon at least a portion of the major surface of the substrate, the patchhaving a thickness and a perimeter, wherein the first coating liquid asdispensed exhibits a viscosity of at least 1 Pascal-sec, optionallywherein a stencil is not used to form the discrete patch.
 2. The processof claim 1, wherein the first coating liquid is dispensed at a shearrate of at least about 1 sec⁻¹, optionally wherein the first coatingliquid is dispensed at a shear rate no greater than about 100,000 sec⁻¹.3. The process of claim 1, wherein the first coating liquid is dispensedat a temperature from about 20° C. to about 100° C.
 4. The process ofclaim 1, wherein the first coating liquid as dispensed exhibits aviscosity from about 2 Pascal-sec to about 20 Pascal-sec.
 5. The processof claim 1, wherein the first coating liquid exhibits at least onedistinguishing rheological characteristic selected from the groupconsisting of thixotropic rheological behavior and pseudoplasticrheological behavior. 6-7. (canceled)
 8. The process of claim 1, whereinthe first coating liquid is a liquid optically clear adhesivecomposition.
 9. The process of claim 8, wherein the liquid opticallyclear adhesive composition comprises a reaction product of: amultifunctional (meth)acrylate oligomer; and a reactive diluentcomprising a monofunctional (meth)acrylate monomer having a viscosity offrom 0.004 to 0.020 Pascal-sec measured at a shear rate of 1 sec⁻¹ and atemperature of 25° C.; and at least one of a plasticizer or amonofunctional (meth)acrylate monomer having alkylene oxidefunctionality. 10-17. (canceled)
 18. The process of claim 1, wherein thepatch covers only a portion of a first major surface of the substrate.19. The process of claim 1, wherein the perimeter exhibits a geometricshape selected from a square, a rectangle, or a parallelogram. 20-21.(canceled)
 22. The process of claim 1, wherein the thickness of thepatch is greater proximate a center of the patch, further wherein thethickness of the patch is lower proximate the perimeter of the patch.23. The process of claim 1, wherein the patch is comprised of at leastone raised discrete protrusion extending outwardly from the majorsurface of the substrate. 24-33. (canceled)
 34. The process of claim 1,wherein the thickness of the patch is substantially uniform, optionallywherein a mean thickness of the patch is from about 1 μm to about 500μm. 35-36. (canceled)
 37. The process of claim 1, wherein the substrateis a light emitting display component or a light reflecting devicecomponent. 38-40. (canceled)
 41. The process of claim 1, wherein thecoating head is selected from the group consisting of a single slot die,a multiple slot die, a single orifice die, and a multiple orifice die.42. The process of claim 41, wherein the coating head is a single slotdie having a single die slot, further wherein the external opening iscomprised of the die slot.
 43. The process of claim 42, wherein thegeometry of the single slot die is selected from a sharp-lippedextrusion slot die, a slot fed knife die with a land, or a notched slotdie. 44-45. (canceled)
 46. The process of claim 1, further comprisingrepeating the steps of claim 1 using a second coating liquid. 47-48.(canceled)
 49. The process of claim 1, further comprising disposing asecond substrate relative to the first substrate such that the patch ispositioned between the first and second substrates, wherein the patchcontacts at least a portion of each of the first and second substrates,thereby forming a laminate.
 50. The process of claim 49, furthercomprising curing the coating liquid by applying heat, actinicradiation, ionizing radiation, or a combination thereof.
 51. The processof claim 50, wherein the laminate comprises an organic light-emittingdiode display, an organic light-emitting transistor display, a liquidcrystal display, a plasma display, a surface-conduction electron-emitterdisplay, a field emission display, a quantum dot display, a liquidcrystal display, a micro-electromechanical system display, a ferroliquid display, a thick-film dielectric electroluminescent display, atelescopic pixel display, or a laser phosphor display.